My 544 B-18 runs smoothly when warmed up, but when cold
it runs very rough, with a put-put-put sound. After a few
minutes running, it smooths out and runs perfectly....
My question: what would allow the B-18 to run perfectly
when warm, but cause it to run rough when cold?

PROBLEM SOLVED: My choke cable was seizing up, not moving carb jets.
Installed new cable and all is well now-- choke cable works so smoothly
that I just want to play with it!! Thanks for everybody's ideas.....
Gjotland

Gj...;

Thanks for follow up to confirm fix...your take-away from this should be to understand that the cold and unchoked mixture was only ignitable and burning in less than all cylinders, with the non-firing ones not contributing any power, hence the rough running...demonstrating how important a properly working choke is once again.

As far as "playing with it" now that it's working well, unless it's really frigid, that is just not necessary after about 30-60 seconds of running and getting some heat into the Cyl Head...

Cheers

Thanks everybody. Yes I pull the choke when cold. After the engine is warmed and runs smoothly, if I again pull out the choke, the idle speed increases so I assumed the choke is working correctly, but after reading your comments I know I should have the choke settings checked by my mechanic. Thanks - I love my
'64 544 !

Gj;

Sign of a proper working Choke is that Jets drop, not that idle rises...idle rising is a secondary result of the adjustment of Fast Idle Screw on its actuator cam. You can study and understand the action of this with Ign Off, by operating Throttle and observing the action of both Jets and Fast Idle Screws on their Cams, as seen here.

Source: http://www.sw-em.com/checkchoke.htm
...and you can adjust the amount of Idle by (very) small adjustments of the screw...no mechanic necessary.

Cheers

Ron -
When I operate the throttle the jets do not move.
When I pull the choke the fast idle screws move away from lever
but again, the jets do not move......mystery to me!
Thanks, Gj

Gj;

"When I operate the throttle the jets do not move." ...they are not expected to!...Gas Pedal moves Throttle Linkage, and that moves Throttle...Choke Linkage moves Jets, or is supposed to when correctly adjusted...not counting Fast Idle, they are separate!

"When I pull the choke the fast idle screws move away from lever
but again, the jets do not move..." ...Fast Idle Adjustment Screw should ride up on Fast Idle Cam as it rotates ClockWise with pull of Choke Cable...it sounds like yours are not adjusted correctly (**)...Loosen Philips Screw to separate Choke Linkage from Cable, and operate the Linkage CW, taking note of action (Jet should drop, and FIAS should ride up on FIC, opening up Throttle slightly...)

Reminder: Carbs are mechanical devices and as such need (and deserve) to be well lubed, so their moving and sliding linkages can function properly through their range of movement. Use a proper grease or graphite filled grease for this, DO NOT spray WD40 on them thinking you have lubed them...if you do this, I cannot help you further...! WD has its place, but not here...it is mostly solvent which leaves very little behind in the way of long-term lubrication (MUCH LESS and way less permanent than is called for here!).

Note: Unlike other (typical downdraught) carbs, there is no accelerator pump which squirts fuel into airflow path each time when operating Throttle Linkage (possibly "flooding" engine at next starting attempts with too much fuel), so it is OK to operate Throttle and/or Choke Linkages with Ign OFF, as many time as you need, to see how they should function ...no jeopardy! (Remove Air Filters for a clear view and access!)

(**) From the questions you are asking, it sounds like you need to familiarize yourself better with the Carbs before attempting Adjustments, so that you truly understand what these linkages and adjustments do...for this, I recommend you read and follow this: http://www.sw-em.com/SU%20Carb%20Service.htm ...once familiar and comfortable with your SUs, you can undertake making adjustments...not before...

See also...Check your Choke tech article: http://www.sw-em.com/checkchoke.htm

Cheers

Thanks Ron, will follow your suggestions,
Gj

Yes.
SUs are some of the simplest yet most misunderstood carburetor.

Once you understand the way they are designed and how they work you'll wonder why people think they're such a mystery.

I will assume that you are pulling out the choke when starting from cold.

Have you checked that the "fast idle" cam and linkage assembly are working when you pull the choke lever?

As Tom says, taking a bit of time getting the choke and fast idle settings set up properly can work wonders. Having the first 1/8" of choke pull just increasing the revs a bit without pulling the jets down is a big plus.

Gj;

As Al and Derek mention, if Choke on one Carb is not enrichening quite as much as the other, those two cylinders may also not be firing nearly as well immediately after starting...so check you Choke settings...I like to see about 1/4" of Jet drop at full Choke linkage pull...

Cheers

Gj;

I'd run it for a few seconds (just long enough to be able to touch exhaust and not get burned, but tell which cylinder(s) are not firing), then pull Spark Plug from the non-firing cylinder inspect, then swap it with one from a firing cylinder to see if issue follows Spark Plug or cylinder...OR...sometimes Spark Plugs need to get some heat into them to burn off deposits and allow a good spark...

Good Hunting

When it’s running rough pull one plug wire at a time to see if you can narrow the miss to a particular cylinder. You may have something like a leaking intake manifold gasket that closes up when the engine gets warm.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)